using primitives
$merge(~+~, bag [1,1,2,2,2], bag [2,2,3,3])
$merge(~.-~, bag [1,1,2,2,2], bag [2,2,3,3])
$merge(~min~, bag [1,1,2,2,2], bag [2,2,3,3])
$merge(~max~, bag [1,1,2,2,2], bag [2,2,3,3])
$merge(~min~, {1,2,3}, {2,4})
$merge(~max~, {1,2,3}, {2,4})
$merge(~.-~, {1,2,3}, {2,4})
$merge(\p. {? (x + y) mod 2 when p is (x,y) ?}, {1,2,3}, {2,4})