# | -- a binary operator, often used for horizontal concatenation

• || -- a binary operator, often used for vertical concatenation

## 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
• GradedModuleMap | GradedModuleMap -- a binary operator, often used for horizontal concatenation
• Iterator | Iterator (missing documentation)
• Array | Array -- see List | List -- join lists, sequences or arrays
• List | List -- join lists, sequences or arrays
• Sequence | Sequence -- see List | List -- join lists, sequences or arrays
• Matrix | Matrix -- join matrices horizontally
• Matrix | Number -- see Matrix | Matrix -- join matrices horizontally
• Matrix | RingElement -- see Matrix | Matrix -- join matrices horizontally
• Number | Matrix -- see Matrix | Matrix -- join matrices horizontally
• RingElement | Matrix -- see Matrix | Matrix -- join matrices horizontally
• RingElement | RingElement -- see Matrix | Matrix -- join matrices horizontally
• Net | Net -- join strings or nets
• String | String -- see Net | Net -- join strings or nets
• String | ZZ -- see Net | Net -- join strings or nets
• ZZ | String -- see Net | Net -- join strings or nets
• ZZ | ZZ -- logical or

## For the programmer

The object | is .

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.