## net.sf.saxon.expr
Interface Negatable

All Known Implementing Classes:
  BooleanExpression, BooleanFn, Existence, ValueComparison

    public interface Negatable

This interface is implemented by expressions that returns a boolean value, and returns an expression whose result is the negated boolean value

Method Summary
`boolean` `isNegatable(ExpressionVisitor visitor)` Check whether this specific instance of the expression is negatable
`Expression` `negate()` Create an expression that returns the negation of this expression

Method Detail

### isNegatable

    boolean isNegatable(ExpressionVisitor visitor)

  Check whether this specific instance of the expression is negatable

  Returns:
    true if it is

### negate

    Expression negate()

  Create an expression that returns the negation of this expression

  Returns:
    the negated expression
  Throws:
    `IllegalOperationException` - if isNegatable() returns false

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