mathematical quinary operator: left sequence notation/converter
Produces the left application of the operation/function a=• on sequence b=b(y(c)), the terms of which are functions evaluated at (possibly dummy) values c (multi-index) belonging to set d (at the values of which the function b is evaluated) taken in order e (rule prescription; note that the application is from the left). The steps at which c's are taken can be specified by d or by taking complicated (evaluated) expressions y of c as arguments of b. Output is in the format (for example: scalar, tensor, function, etc.) that the operation a=• yields. For Sigma/series summation notation, a=+, for Pi multiplication notation a=×, for functional power/iterated composition of functions a=°, for the Cartesian product of sets a=× (preferred to "exponentiation of sets" notation like An).