/* Function that loops over multiple arrays simultaneously depending on the list with less length */
lomas(L):=block(
    minlen:lmin(map(length,L)),
    makelist(makelist(L[i][j],i,1,length(L)),j,1,minlen))$

/* Test case */
lst:[[a,b,c],[A,B,C],[1,2,3]]$
lomas(lst);