in the art will recognize the piston 24 has moved toward the slips and element causing those components to take on a set position upon the temperature falling to a level below the phase change point of the pcm and assuming that the particular embodiment does not contain slips that permanently bite into a surface against which they set then the retraction of the piston 24 will cause the other components of the tool to revert to the run in position whereby retrieval of the tool is facilitated increasing the temperature of the pcm may occur in any of the processes noted above or may be effected by a heating element 26 see fig2 in thermally communicative position relative to the pcm in another embodiment the pcm is employed as a part of an actuation operation rather than to independently cause the actuation operation more specifically referring to fig4 it will be appreciated that the components 10 12 14 16 and 24 are essentially the same and are not redescribed but that the balance of the tool has changed directing attention to the left side of the drawing the piston 24 is seen to be in contact with a pcm 30 similar to the foregoing embodiment but it is also in contact with a stop 32 the stop 32 will prevent the pcm 30 when in solid form from exerting any force on the piston 30 regardless of the position of a.