If `t` is false, then the code in `u` is not evaluated.

- Expression and Expression, see Expression -- the class of all expressions
- Expression and Holder, see Expression -- the class of all expressions
- Expression and Thing, see Expression -- the class of all expressions
- Holder and Expression, see Expression -- the class of all expressions
- Holder and Holder, see Expression -- the class of all expressions
- Thing and Expression, see Expression -- the class of all expressions

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

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

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