Documentation for routine i assembled from the following pages:

Language documentation: Terms §

From Terms

(Terms) term i §

Returns the imaginary unit (for Complex numbers).

Class: Complex §

From Complex

(Complex) postfix i §

Adding a trailing i to a number literal makes it a Complex, for example:

say 2i;     # same as Complex.new(0, 2); 
say 1-2e3i; # same as Complex.new(1, -2e3);