[a]*/[b][[...*/c]]
where [a], [b], and [c] are all values
[a], [b], and [c] are numbers
returns the root of [a] by [b], then by [c] in the most precise type that appears in the chain
root(type[a], type[b], type[c]) is defined
returns a call of [a], [b], and [c] to root
[a]*/[b] is defined
evaluates [a]*/[b] first, then evaluates the rest of the expression