/*random*/
/*Random number generator
Alan Bundy 22.11.79*/

/*Get random Num in Range*/
random(Range,Num) :-
        seed(Seed), random(Range,Seed,Num).

/*Get Num ffrom Seed first time*/
random(Range,Seed,Num) :- Num is (Seed mod Range) + 1.

/*Grow Num on subsequent occasions*/
random(Range,Seed,Num) :-
        NewSeed is 125*Seed + 1,
        random(Range,NewSeed,Num).

/*random number seed*/
seed(13).

/*Choose random element of list*/
random_pick(List,El) :-
        length(List,L), random(L,N), nth(N,List,El).

/*find nth element of a list*/
nth(1,[Hd|Tl],Hd) :- !.

nth(N,[Hd|Tl],El) :-
        N>1, !, N1 is N-1,
        nth(N1,Tl,El).