factorial(N) <- 1 if N =< 0. factorial(N) <- N * factorial(N-1) if N > 0. double( N ) <- N*2. quadruple( N ) <- double( double(N) ). append( [], L ) <- L. append( [H|T], L ) <- [ H | append(T,L) ]. count( L ) <- 0 if L = []. count( [H|T] ) <- 1 + count( T ). converse does write_list(reply_to(readline('?'))) and converse. divides_by_4( N ) if ( N/2 rem 2 ) = 0.