<== -- a unary and binary operator

Ways to use symbol <== :

Expression <== Expression -- see Expression -- the class of all expressions
Expression <== Holder -- see Expression -- the class of all expressions
Expression <== Thing -- see Expression -- the class of all expressions
Holder <== Expression -- see Expression -- the class of all expressions
Holder <== Holder -- see Expression -- the class of all expressions
Thing <== Expression -- see Expression -- the class of all expressions

For the programmer

The object <== is a keyword.

This operator may be used as a binary operator in an expression like x<==y. The user may install binary methods for handling such expressions with code such as

         X <== Y := (x,y) -> ...

where X is the class of x and Y is the class of y.

This operator may be used as a prefix unary operator in an expression like <==y. The user may install a method for handling such expressions with code such as

           <== Y := (y) -> ...

where Y is the class of y.