# Symbolic Connectivity Layers

Use the symbol table to specify derived layers and to assign names to layer/datatype combinations. A symbolic layer must have a name which can be used in the connectivity table instead of the original layers. In addition, an expression must be specified that defines the contents of the layer.

Inside the expressions

- Use "layer/datatype" notation to specify an original layer with explicit GDS layers and datatypes.
- Use the name to specify a named original layer or to refer to a symbolic layer defined in another entry.
- Use the operators '+', '*', '-' and '^' to specify logical OR, AND, NOT and XOR respectively. The precedence of evaluation is '^' and '*' before '+' and '-'.
- Use round brackets to group expressions.

Examples:

17 | Abbreviation for GDS layer 17, datatype 0
2/0*17/0 | Logical AND between layer 2 and 17, both datatype 0
2*(5+7) | Logical AND between layer 2 and the logical OR combination of 5 and 7
ACTIVE-POLY | Logical NOT between the symbolic layer ACTIVE (defined in another entry) and POLY (also defined in another entry).