Dear Gap-Forum,

The GAP3.4.4 (DOS) code below gives a strange result: the semidirect
product's size differs before and after printing its elements. If printing
is omitted, the sizes agree (12).

What causes this? Thankx.

Bruce

----------------------------------

G := SymmetricGroup(3);
f := IdentityMapping(G);
N := CyclicGroup(2);
sdp := SemidirectProduct(G,f,N);
Print("Size1 ",Size(sdp));
[...]
The problem here seems to be that the function SemidirectProduct
apparently gets confused...
(indeed, the input data doesn't really make sense here)

Nevertheless, the behavour is amusing (same under UNIX): indeed:
gap> G := SymmetricGroup(3);                    
Group( (1,3), (2,3) )
gap> N := CyclicGroup(2);                       
Group( (1,2) )
gap> f := IdentityMapping(G);                   
IdentityMapping( Group( (1,3), (2,3) ) )
gap> Size(SemidirectProduct(G,f,N));            
12
gap> Length(Elements(SemidirectProduct(G,f,N)));
36
gap> Size(Elements(SemidirectProduct(G,f,N)));
36
gap>

Probably it's a bug rather than a feature :-)
Regards,
d.pasechnik@twi.tudelft.nl