fact: Definition gmap_curry `{Countable K1, Countable K2} {A} : gmap (K1 * K2) A → gmap K1 (gmap K2 A) := map_fold (λ '(i1, i2) x, partial_alter (Some ∘ <[i2:=x]> ∘ default ∅) i1) ∅.
imports: stdpp(mapset pmap) stdpp(options)