n-ary mekso operator: for an input of ordered list of ordered pairs ((X1, Y, it outputs formal generalized rational function (x - X1)^Y in the adjoined indeterminate (here: x).
n may be infinite, under the condition that the function is well-defined. In the definition, adjacency of terms denotes multiplication in the relevant algebraic structure. If there is an i such that Yi is omitted, then Yi = 1 by default. For any i, there is no constraint on the values which may be taken by Xi or Yi. See also: "po'i'oi".