There is a set of combinators which traverse three sequences triple-wise. If one sequence is shorter than the others, then only the prefix having the length of the minimum of the three is examined.
3each ( ... seq1 seq2 seq3 quot: ( ... elt1 elt2 elt3 -- ... ) -- ... )

3map ( ... seq1 seq2 seq3 quot: ( ... elt1 elt2 elt3 -- ... newelt ) -- ... newseq )

3map-as ( ... seq1 seq2 seq3 quot: ( ... elt1 elt2 elt3 -- ... newelt ) exemplar -- ... newseq )