Introduction
to Tessellations by Dale Seymour and Jill Britton. Dale Seymour
Publications 1989
This book is aimed primarily at a
‘layman’ in tessellations (as given in their preface), although perhaps more
correct is that of school age level, of the 12-14+ age range. As the title
suggests, this primarily concerns the basic mathematical aspects of tessellations
per se, such as the symmetry operations involved, and simple tessellation
aspects, such as why all triangles and quadrilaterals tessellate. As such, for
this age range this is fine, and as an introduction to the subject serves
admirably.
Another aspect to the book of more concern to readers of this site is that of creating
Escher-like art, Chapter 7, ‘Creating Escher-like tessellations’, of which, in
contrast to the above, I discuss in detail and depth. Pleasingly, this is at
least of a substantial nature, of no less than 53 pages, and this in itself is
to be welcomed (with other publications treating the matter decidedly more cursorily,
often in a handful of pages, which is wholly inadequate). However, this is
somewhat disappointing in its inherent quality, with some very poor
illustrative material, almost all lacking in quality. Broadly, the chapter
discusses two aspects of Escher-like tessellation, somewhat confusingly
intermingling, rather than as distinct aspects. Firstly, this discusses (or purports
to) the 'creation' of 13 of Escher's periodic drawings. Secondly, the creation
of original tessellations, with numerous examples from a variety of nine
different students with an artistic/mathematical bent. However, although in
theory this should make for an interesting discussion as to the procedures, in
practice this is lacking in many ways, and is strictly incorrect. Below I
discuss these two aspects:
1. Escher's Periodic Drawings
The all-important attempts at unravelling Escher's method falls woefully short.
Seymour and Britton purports to illustrate this with 13 examples of Escher's
periodic tessellations (see table below for details). For each periodic drawing
this is then analysed, with a line-for-line recreation. The impression given is
that Escher spontaneously and simply chose an appropriate ‘squiggly line’ that
which was immediately and without further refinement proved suitable for an
animal-like motif. (Indeed, such a method is the premise of the whole chapter,
with other artists examples shown following the same procedure.) Quite simply,
this is not how Escher went about such matters of design his motifs, the method
given being far too advanced, even for Escher's powers of imagination. The
imagination required to draw at least two distinct lines that are 'perfect'
i.e. of life-like form when assembled of a given geometric tessellation is
simply not possible. Granted, on page 188 Britton states
…modify the sides of the polygon until its contour resembles that object…
but not a single diagram shows this! All the diagrams are of a finished line.
Curiously, it is little-known how Escher went about this. More correct is that
Escher started with a geometric shape that tessellates, and then by trial and
error developed and refined this, until finally arriving at a finished motif.
Visions of Symmetry, page 111 shows how the tessellation of ‘Horseman’
developed. The procedure of Britton’s interpretation at prima facie, is simply
incorrect.
2. Students’ Tessellations
A very curious occurrence with these students’ efforts is with the sheer number
of the lower category of difficulty of ‘head’ type (see my Essay 6, Categories
of Difficulty). Indeed, no less than 22 out of the 32 tessellations are of this
type, a massive 68% of the output, with no concession made to this lower
quality category in the writing. A moment’s consideration will show that these
are much simpler to achieve than a whole-body motif. Compare the complexity of
a whole body motif, with say, a quadruped, with head, neck, body, legs, and
tail, with just a single head. Largely here, this difficulty is swept away,
with just the head shown. Furthermore, even within this basic category, there
are many undeserving examples here, these mostly being embellishments. No other
tessellation artists, even those who lean towards this category come anywhere
near this total in percentage terms. Compare this to the top tessellators,
Bailey, Bilney, Nakamura and Scalfittura who do not show any. Other top tessellators, such as Crompton, Escher, and Nicolas show
either just one or two, and for specific, recognisable motifs, such as Sherlock
Holmes, rather than these ‘arbitraries’ here. As a genre we ignore these, with
the implication that these are unworthy of the art. Perhaps one could argue
that in a book of this nature, aimed at the layman, one is cavilling here.
However, it would surely not be asking too much to qualify these with just a
few lines that as a category they are of a decidedly lesser nature in
comparison to a whole bodied motif, but no such qualification occurs.
Another concern is with the inherent quality of the tessellations. Most of the
examples can be described derogatorily as embellishments, or ‘shapes with
eyes’, with all that the artist has done is to add animal-like elements to an
outline that does not bear any resemblance to the creature it is portraying.
Indeed, I classify a substantial number of these, no less than 20 out of 32,
62%. To give an actual example, Dog Head with Bow Tie, page 196, by Lyda
Kobylansky. At first glance, does the tile outline really give the impression
of a dog’s head? No. All it is just an arbitrary shape, with the addition of
dog-like detail i.e. embellishment. (Many others are of the same ilk, see
table.) There is a world of difference in quality and difficulty between a tile
outline that resembles a dog and a tile with dog embellishment! Ironically, on
page 234 Britton give an illuminating quote from personal correspondence by
George Escher (Escher’s son) on this matter:
Do
not confuse the creation of a meaningful contour with highlighting of the
interior tile. These are fundamentally different things. Almost anyone can take
a random shape and draw something lifelike inside its outline. But it is
entirely a different story to push a recalcitrant outline into a pattern that
suggest, without highlighting, some living thing. Highlighting may be necessary
to clarify a decision, is it a bird or fish? But it is often not even
necessary, if the contour is characteristic enough. This discussion is not new…
Excellent advice! Why didn’t these artists listen? Again, perhaps I am being
unfair here, in that it is difficult to emulate Escher in quality. However,
that should not mean that one should not at least try! Even if one can only do
inferior categories and examples, these should not be passed of as ‘equal’ to
Escher’s in worth, which is the general impression given here.
Another feature of the tessellations is the lack of
colour or shading to aid in distinguishing the motifs. Indeed, not a single
tessellation is of this type, all these being of the inferior wireframe type.
Again, the reason for this is not given. The impression thus given is that as a
type i.e. wireframe, these are acceptable. Unfortunately this is not so, as by
their very nature the drawing is rendered inconvenient to view, in that the
motifs are not readily discerned. This aspect is all the more important when
lower quality tessellations are shown, as here. A typical example is ‘Cartoon
Head’ by Steve Dawson. Can you really determine what this is at first, or
indeed second, glance? No. The eye has to ‘struggle’ as it were. As a courtesy
to the viewer, it should be discernable immediately so. Simple contrasting
colours or shading would greatly assist here, even for lower quality examples.
In connection with this, better would have been to emphasise the outside line
of the motif with a thicker line than the interior. All the diagrams are of
lines of unit thickness, which again, with issues of discernment arising. As
guidance to best policy, compare these tessellations with Escher’s own. Did he
do any wireframe types? No. There is a reason. However, in the artist’s
defence, this may have been occasioned by the editors of the book requiring a
simple format suitable for printing in a largely uniform manner, these being
taken from a previous competition, of a standardised format, of the above
wireframe type. Even so, this should not negate the inherent quality aspect
afforded by such types. These should at least be qualified, but again, not so.
A slightly lesser concern is that none of these are titled, or catalogued,
which makes referring these to inconvenient. Consequently, for descriptive
purposes I give these my own titles. Although it may be thought unnecessary,
when lower quality examples are shown, as here, titling is even more necessary.
For example, how best to describe the lower example on page 188 by Steve
Dawson? Pig snout fish with wings? Seahorse with wings? It might even be
something else.
The main shortcoming of the
tessellations shown is their inherent lack of quality, with the various artists
lacking any insight in Escher-like art. Furthermore, the presentation is
lacking, with the diagrams mostly of lines of unit thickness, rendering the
motifs difficult to view with ease, forcing the viewer to scrutinise these as
to ‘what’s what’. These would have been improved by the simple process of
emphasis in their outline. However, this may have been occasioned by the
editors of the book, a detailed above. Even so, this should not negate the
inherent quality aspect.
Critiques of Tessellations
Having assessed the chapter in a broad-brush manner, below I give a
general discussion of each individual tessellation. For the sake of
succinctness, I summarise in a few stock phrases:
§ A shape with …-like elements added.
This is intended to be of a derogatory nature, applied to a tessellation
of the lowest possible quality. All the artist has done is to add life-like
interior detail to a shape bearing not the slightest resemblance to the motif
it is portraying.
§ …but
only due to the talents of the artist in extracting something recognisable from
an arbitrary shape
This in essence follows on from the ‘a shape with ...-like elements
added’ in that the artist has been able to extract something recognisable from
poor raw material
§ Somewhat
far-fetched…
Applied derogatorily to a tessellation where a ridiculous, contrived
creature is formed of different contrary elements, such as a woman’s head with
a pig’s snout.
§ Whimsy
Applied to a tessellation of ‘disjoint’ aspects, with elements taken
from different creatures, of which although possessing shortcomings has some
limited degree of merit, in that it is at least broadly ‘believable’.
§ What
can I say…
Applied to tessellations that are so bad that words should not be
necessary, in that the shortcomings are so obvious as to not need commenting
upon.
1. Horse Head. Anonymous. Page 137
Poor. A shape with horse-like elements added. Cartoon-like,
with conflicting perspectives, with the head seen in profile, with the eye
straight on. The underside of the head has a strange gouge. Furthermore, a
horses’ head in profile is not like this. Note the difficulty in identifying
the motif here.
2. Witches Head, by Steve Dawson. Page 188
Poor. A shape with witch-like
elements added, but only due to the talents of the artist in extracting
something recognisable from an arbitrary shape. Loosely, yes, as titled, but of
the easiest tessellation type (head).
3. Winged Seahorse by Steve Dawson. Page 188
Poor. A seahorse with wings? Possibly, but only as a fantasy. Somewhat
far-fetched…
4. Dog Head, by Tracy Steszyn. Page 189
Poor. A shape with cartoon like dog-like elements added.
5. Woman’s Head, by Christina Jams. Page 189
Unacceptable. A shape with
woman-like head elements added. The body is formless…
6. ‘Mutant Beast with Open Mouth’ Head, by
Steve Dawson. Page 190
Unacceptable. A shape with
‘mutant beast-like’ elements added. Slightly like a ‘mutant beast with
open-mouth’, but still broadly a shape with beast-like elements added.
7. Mutant Elephant Head With Human-like
Features, by Steve Dawson. Page 190
Unacceptable. A shape with
mutant elephant-like elements added. Various uncertainties arise - does this
possess horns or is this horn-like appearance actually part of the neck? An
emphasised outline would negate this ambiguity. Has a human-like mouth.
Somewhat far-fetched…
8. ‘Hockey Players of Unidentifiable
Creature’, by Steve Dawson. Page 191
Poor. The creature is unrecognisable, loosely described as of a
‘mouse-like head, wearing a floppy hat and scarf, with a human body holding a
hockey stick’. Assuming that this is as I presume, a most unlikely combination,
with no unifying features – just why should a mouse-like head, complete with a
floppy hat and scarf, with a human body holding a hockey stick, be… However, as
a ‘whimsy’, this is quite acceptable and is one of the ‘better’ tessellations
here, as anatomically, despite the unlikely constituents, there are no obvious
inconsistencies – everything is in proportion. Somewhat far-fetched…
9. Dog Head. Anonymous. Page 194
Poor. A shape with dog-like elements added. A lack of dog anatomy is evident
here – the mouth is portrayed incorrectly, and the left ear is somewhat
human-like. However, this matter aside, the detail does indeed resemble a dog’s
head. However, this is only due to the talents of the artist in extracting
something recognisable from an arbitrary shape.
10. Eagle Head, by Lyda Kobylansky. Page 195
Poor. A shape with eagle-like elements added.
11. Horse Head with Antlers, by Henry
Furmanowicz. Page 195
Poor. A reasonable attempt at a horse head, as it does indeed bare a likeness,
albeit let down by strange antler-like protrusions above the head.
12. Dog Head with Bow Tie, by Lyda
Kobylansky. Page 196
Poor. A shape with a cartoon dog-head-like elements added. Why should a dog be
wearing a bow tie…? Loosely identifiable as a dog head. However, this is only
due to the talents of the artist in extracting something recognisable from an
arbitrary shape.
13. Pirate Head, by Nick Zannella. Page 196
Poor. A shape with pirate-like elements added. This example is worth more
praise than others are, as by the skill of the artist a reasonable pirate
emerges from unpromising raw material.
14. Cartoon Head, by Steve Dawson. Page 197
Poor. A shape with human-like cartoon elements added. However, this is
only due to the talents of the artist in extracting something recognisable from
an arbitrary shape.
15. Bird, by Henry Furmanowicz. Page 197
Reasonable. In contrast to most of the examples, one of the better ones
here, with an outline that does indeed truly resemble a recognisable creature,
a bird. A pleasing aspect to detail is that the wings are, or at least implied,
anatomically correct, with serrations to the rear, as is the tail. This though
may just be accidental… However, its let down somewhat as being over detailed,
as a bird is not evident at first glance, being lost in a myriad of detail.
16. ‘Rabbit Head’ and ‘Creature with Bowtie
Head’, by Steve Dawson. Page 200
Reasonable. A shape with head-like elements added. A relatively pleasing
innovation is of two different interiors, but this is militated against in that
the tile is really just an arbitrary shape. Both shapes with head-like elements
of a cartoon-like nature added. Although of a weak category, as a ‘whimsy' the
rabbit-like creature is pleasing.
17. Bird, by Jill Britton. Page 204
Reasonable. Loosely bird-like, especially so concerning the head.
18. Moose Head, by Steve Dawson. Page 205
Poor. A shape with cartoon moose-like elements added. However, this is only due
to the talents of the artist in extracting something recognisable from an
arbitrary shape. As a ‘whimsy’, reasonable.
19. Rogue in a Plumed Hat Head, by Steve
Dawson. Page 205
Unacceptable. A shape with a few rogue elements added. However, this is
only due to the talents of the artist in extracting something recognisable from
an arbitrary shape. As a whimsy, reasonable.
20. ‘Pirate’, by Jill Britton. Page 208
Poor. A shape with pirate-like elements added. A lack of defining outline
renders this most inconvenient.
21. Bird, by Steve Dawson. Page 209
Reasonable. Loosely bird-like. The detail on the wings displays a lack
of anatomical knowledge.
22. Dog Head –‘Tisha’, by Stephen Makris.
Page 212
Poor. A shape with cartoon like dog-like elements added. However, this is only
due to the talents of the artist in extracting something recognisable from an
arbitrary shape. As a whimsy, reasonable.
23. Duck, Bird, Mutant Horse, Goblin, Dragon,
and Cuckoo Heads, by Steve Dawson. Page 213
Unclassified. Firstly, as this is in two parts, with single motifs and a
tessellation, I discuss separately.
Single motifs ‘Possibilities’:
A shape with head-like elements of different creatures added, of five heads,
and one whole bird creature. Mostly dreadful. The one example of relative worth
is ‘duck’, which as a whimsy, reasonable. All Dawson
has done here is to add multiple head details to an arbitrary shape. The
impression given here is one of inventiveness, as a single tile has multiple
motifs. However, many other heads can be added in a like manner, rendering the
number meaningless.
Tessellation:
A shape with dragon-like elements added. The skill of the artist results in a
reasonable dragon head.
24. Hummingbird, by Jill Britton. Page 216
Poor. A shape with hummingbird-like beak element added. At least the
beak is portrayed accurately. This has similarities with one of Peter Stevens’s
birds, in a different book, of which he is listed in the references.
25. Clown Head, by Jill Britton. Page 219
Reasonable. A shape with cartoon-like clown-like elements added. However, this
is only due to the talents of the artist in extracting something recognisable
from an arbitrary shape. Of its type, of a lower tariff of difficulty, quite
pleasing, with no obvious shortcoming per se.
26. Devil Head, by Steve Dawson. Page 222
Reasonable. A shape with cartoon-like devil-like elements added. Again,
of its type, of a lower tariff of difficulty, quite pleasing, with no obvious
shortcoming per se, albeit it is not clear as to outline, as the beard and hair
are vague.
27. Fish, by Jill Britton. Page 225
Reasonable. Fish-like in outline, of a reasonable quality fish, albeit the
upper fins are not streamlined.
28. Dogs, by Jill Britton. Page 229
Reasonable. A dog lying down. This has likeness to the St Bernard tessellation
of Joseph Teeters. A reasonable tessellation if indeed of originality, less so
if ‘after Teeters’. One of the better ones if indeed it is original.
29. Owl, by Steve Dawson. Page 230
Poor. A shape with owl-like elements added. However, this is only due to
the talents of the artist in extracting something recognisable from an
arbitrary shape The one redeeming feature of this is the head, with tufted
ears, as in a real-life owl.
30. Sea
Lion, by Steve Dawson. Page 230
Poor. A shape with sea
lion-like elements added. However, this is only due to the talents of the
artist in extracting something recognisable from an arbitrary shape
31. Birds, by Jill Britton. Page 233
Reasonable. At first glance reminiscent of Escher’s No 44, but is indeed
distinct, with different symmetries.
32. Woman’s Head with Pig-like Nose, by
Sheila Le Blanc. Page 233
Unacceptable. A shape with cartoon-like pig-like snout and human
elements added. Somewhat far-fetched. What can I say…
Summary
The main shortcoming of the Escher-like tessellations is their inherent
lack of quality, with the various artists lacking any insight in Escher-like
art. The majority are essentially worthless. Very few are of any note, and even
when recognisable, they still lack inherent quality. Predominant are the
inferior category ‘head’ types, with no concession made to this easier
category. Worse, the various artists still struggle with achieving believable ‘heads’.
Furthermore, the presentation is lacking, without colour or shading, with the
diagrams, wireframes, of lines of unit thickness, rendering the motifs
difficult to view with ease, forcing the viewer to scrutinise these as to ‘what’s
what’. These would have been improved by the simple process of emphasis in
their outline. However, as discussed above this may not have been dictated by
the artists themselves.
A lack of critiquing is evident throughout (though that said, nearly all
artists do not critique their tessellations. Why not?). This is regrettable, in
that the impression given is that these are the ideal to aim for, and so
inferior ones are perpetuated by the reader with the belief that these are
‘good’.
Perhaps one could argue that due to the youth and inexperience of the artists
one could, and indeed should expect inferior standards. Well yes, but why show
these? Al this is all the more surprising given the quote near the end of the
book, page 234:
Do not confuse the
creation of a meaningful contour with highlighting of the interior tile.
Where all the evidence is that the artists have!
|
Table of Escher-Like Tessellations in Introduction
to Tessellations by Dale Seymour and Jill Britton
N.B. All these are of a wireframe type
|
|
|
Number
|
|
Artist
|
|
Motif
|
|
Page
|
|
Head
only
|
|
Embellishment
|
|
|
1
|
|
Anonymous
|
|
Horse
Head
|
|
137
|
|
Yes
|
|
Yes
|
|
|
2
|
|
Steve
Dawson
|
|
Witch
Head
|
|
188
|
|
Yes
|
|
Yes
|
|
|
3
|
|
Steve
Dawson
|
|
Sea
Horse with Wings?
|
|
188
|
|
No
|
|
Yes
|
|
|
4
|
|
Tracy
Steszyn
|
|
Dog
Head
|
|
189
|
|
Yes
|
|
No
|
|
|
5
|
|
Christina
Jams
|
|
Woman’s
Head
|
|
189
|
|
Yes
|
|
Yes
|
|
|
6
|
|
Steve
Dawson
|
|
Mutant
Head
|
|
190
|
|
Yes
|
|
Yes
|
|
|
7
|
|
Steve
Dawson
|
|
Mutant
Elephant Head
|
|
190
|
|
Yes
|
|
Yes
|
|
|
8
|
|
Steve
Dawson
|
|
Mutant
Mouse with Hockey Stick
|
|
191
|
|
No
|
|
No
|
|
|
9
|
|
Anonymous
|
|
Dog
Head
|
|
194
|
|
Yes
|
|
No
|
|
|
10
|
|
Lyda
Kobylansky
|
|
Eagle
Head
|
|
195
|
|
Yes
|
|
Yes
|
|
|
11
|
|
Henry
Furmanowicz
|
|
Horse
Head with Antlers
|
|
195
|
|
Yes
|
|
No
|
|
|
12
|
|
Lyda
Kobylansky
|
|
Dog
Head with Bowtie
|
|
196
|
|
Yes
|
|
Yes
|
|
|
13
|
|
Nick
Zannella
|
|
Pirate
Head
|
|
196
|
|
Yes
|
|
Yes
|
|
|
14
|
|
Steve
Dawson
|
|
Cartoon
Head
|
|
197
|
|
Yes
|
|
Yes
|
|
|
15
|
|
Henry
Furmanowicz
|
|
Bird
|
|
197
|
|
No
|
|
No
|
|
|
16
|
|
Steve
Dawson
|
|
Rabbit
Head/‘Goofy’ Head
|
|
200
|
|
Yes
|
|
Yes
|
|
|
17
|
|
Jill
Britton
|
|
Bird
|
|
204
|
|
No
|
|
No
|
|
|
18
|
|
Steve
Dawson
|
|
Goofy
Moose Head
|
|
205
|
|
Yes
|
|
Yes
|
|
|
19
|
|
Steve
Dawson
|
|
Rogue
in a Plumed Hat Head
|
|
205
|
|
Yes
|
|
Yes
|
|
|
20
|
|
Jill
Britton
|
|
Pirate
|
|
208
|
|
No
|
|
No
|
|
|
21
|
|
Steve
Dawson
|
|
Bird
with Crest
|
|
209
|
|
No
|
|
No
|
|
|
22
|
|
Stephen
Makris
|
|
‘Tisha’
Dog Head?
|
|
212
|
|
Yes
|
|
Yes
|
|
|
23
|
|
Steve
Dawson
|
|
Dragon
(with 5 variations)
|
|
213
|
|
Yes
|
|
Yes
|
|
|
24
|
|
Jill
Britton
|
|
Hummingbird
|
|
216
|
|
No
|
|
No
|
|
|
25
|
|
Jill
Britton
|
|
Clown
Head
|
|
219
|
|
Yes
|
|
Yes
|
|
|
26
|
|
Steve
Dawson
|
|
Devil
Head
|
|
222
|
|
Yes
|
|
Yes
|
|
|
27
|
|
Anonymous
|
|
Fish
|
|
225
|
|
No
|
|
No
|
|
|
28
|
|
Jill
Britton
|
|
Dogs
|
|
229
|
|
No
|
|
No
|
|
|
29
|
|
Steve
Dawson
|
|
Owl
|
|
230
|
|
Yes
|
|
Yes
|
|
|
30
|
|
Steve
Dawson
|
|
Seal
|
|
230
|
|
Yes
|
|
Yes
|
|
|
31
|
|
Jill
Britton
|
|
Bird
|
|
233
|
|
No
|
|
No
|
|
|
32
|
|
Sheila
Le Blanc
|
|
Woman
Head with Pig’s Nose
|
|
233
|
|
Yes
|
|
Yes
|
|
|
Frequency:
Steve Dawson (14)
Jill Britton (7)
Anonymous (2)
Lyda Kobylansky (2)
Henry Furmanowicz (2)
Tracy Steszyn (1)
Christina Jams (1)
Nick Zannella (1)
Stephen Makris (1)
Sheila Le Blanc (1)
Totals:
Heads (22)
Whole Body (10)
Embellishments:
Yes (20)
No (12)
|
Table of Escher’s Prints used in Dale
Seymour and Jill Britton’s Book Introduction to Tessellations
|
|
|
Number
|
|
Page
|
|
Print/Periodic
Drawing
|
|
Wireframe
Analysis
|
|
|
1
|
|
15
|
|
Sun
and Moon
|
|
No
|
|
|
2
|
|
184
|
|
Reptiles
|
|
Yes,
185
|
|
|
3
|
|
186
|
|
Pegasus
PD
|
|
Yes,
187
|
|
|
4
|
|
192
|
|
Fish
PD
|
|
Yes,
193
|
|
|
5
|
|
198
|
|
Lizard
PD
|
|
Yes,
199
|
|
|
6
|
|
201
|
|
Lizard
PD
|
|
Yes,
202
|
|
|
7
|
|
206
|
|
Reptiles
PD
|
|
Yes,
207
|
|
|
8
|
|
210
|
|
Bird
PD
|
|
Yes,
211
|
|
|
9
|
|
214
|
|
Lizards
PD
|
|
Yes,
215
|
|
|
10
|
|
216
|
|
Metamorphosis
I
|
|
No
|
|
|
11
|
|
217
|
|
Chinamen
PD
|
|
Yes,
217, 218
|
|
|
12
|
|
220
|
|
Crabs
PD
|
|
Yes,
221
|
|
|
13
|
|
223
|
|
Dogs
PD
|
|
Yes,
224
|
|
|
14
|
|
226
|
|
Pessimist/Optimist
PD
|
|
Yes,
226
|
|
|
15
|
|
227
|
|
Swans
PD
|
|
Yes,
228
|
|
|
16
|
|
231
|
|
Horseman
PD
|
|
Yes,
231
|
|
|
Agree or disagree? Email me
Created:
26 September 2009. Updated,
revised and enlarged: 30 August 2010,
25, 29 June 2012