Original sentence: Market-oriented economists claim that the fallacy occurs when it is assumed that a variable (such as "labor") is fixed; in contrast, they claim that it is subject to endogenous change.The lump of labor fallacy, also called the fallacy of labor scarcity, is a purported fallacy in economic reasoning
Edited sentence: The fallacy occurs when it is assumed that a variable (such as "labour") is fixed when in reality it is subject to endogenous change, determined for instance by a model.The lump of labour fallacy, also called the fallacy of labour scarcity in the most restricted sense is a fallacy in economic reasoning