Note that it is possible the "math" expression in the Delay contains literal numbers or parameters with undeclared units. In those cases, it is not possible to calculate the units of the overall expression without making assumptions. LibSBML does not make assumptions about the units, and Delay::getDerivedUnitDefinition() only returns the units as far as it is able to determine them. For example, in an expression X + Y, if X has unambiguously-defined units and Y does not, it will return the units of X. When using this method, it is critical that callers also invoke the methodDelay::containsUndeclaredUnits()to determine whether this situation holds. Callers should take suitable action in those situations.
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