freeze replaces its argument, expr (not a complex or real numeric constant, a name, or a string), with a name of the form freeze/R0, freeze/R1, ...

To return the original expression the thaw function must be used.

This can be used to prevent parts of an expression from being subjected to the effects of symbolic manipulation.

$z≔\mathrm{freeze}\left(x+y\right)$

$z≔\mathrm{freeze/R0}$

$\mathrm{thaw}\left(z\right)$

$x+y$

$e≔\cos \left(2x\right)+\sin \left(a+b\right)$

$e≔\cos \left(2x\right)+\sin \left(a+b\right)$

$\mathrm{expand}\left(e\right)$

$2{\cos \left(x\right)}^2-1+\sin \left(a\right)\cos \left(b\right)+\cos \left(a\right)\sin \left(b\right)$

$\mathrm{subs}\left(2x=\mathrm{freeze}\left(2x\right)\,e\right)$

$\cos \left(\mathrm{freeze/R1}\right)+\sin \left(a+b\right)$

$\mathrm{expand}\left(\right)$

$\cos \left(\mathrm{freeze/R1}\right)+\sin \left(a\right)\cos \left(b\right)+\cos \left(a\right)\sin \left(b\right)$

$\mathrm{thaw}\left(\right)$

$\cos \left(2x\right)+\sin \left(a\right)\cos \left(b\right)+\cos \left(a\right)\sin \left(b\right)$