Forms of conditionals

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The conditionals used in $If and $Ifi statements can be of many forms. The principal ones involve:

•	Comparisons involving control variables or environment variables testing whether a variable is defined or whether its contents match a string.

•	Characteristics of a named item testing its type, set dependency or declaration status.

•	GAMS command line parameters including user defined options.

•	The settings of system characteristics.

•	Batinclude parameters testing existence, contents, declaration status, or type.

•	Error checks.

•	File existence status.

Each is discussed below.