Prolog - copy a piece of list

Question

I need to duplicate list in prolog.

I have list:

L = [a(string1,value1),a(string2,value2),a(string3,value3),a(string4,value4)].

Out

Answer 1

pattern matching is used to decompose arguments: you can do

copy([],[]).
copy([a(H,_)|L1],[H|L2]) :- copy(L1,L2).