Define the default symbol for the imaginary unit, that is, the square root of negative one. The default Unicode codepoint for the imaginary unit. (DOUBLE-STRUCK ITALIC SMALL I)
\u2148 := <<IMAGINARY_UNIT>>
Also used for the imaginary unit (especially by electrical engineers, who use "i" to indicate current. (DOUBLE-STRUCK ITALIC SMALL J)
\u2149 := <<IMAGINARY_UNIT>>
Redefine the letter "i" to also be the imaginary unit
i := \u2148
