to --Command, special form, see below.
     This command takes a variable number of inputs. The first is the name
     of a procedure to be defined. The rest, if any, must be preceded by
     colons, and are the names of variables to be used as inputs to the
     procedure. Logo responds to the to command by printing a "greater
     than" sign (>) prompt, to show you that you are defining a procedure
     rather than entering commands to be executed immediately. You type
     the instruction lines which make up the definition. When you are done
     with the definition, type the special word end on a line by itself.
     For example:

     _*to twoprint :thing
     _>print :thing
     _>print :thing
     _>end
     _*

     This example shows the definition of a procedure named twoprint, which
     has one input, named thing. The procedure you are defining with the
     to command must not already be defined.