... is the chain rule. Straight continuous lines differentiate downwards (integrate up) with respect to the main variable (in this case ), and the straight dashed line similarly but with respect to the dashed balloon expression (the inner function of the composite which is subject to the chain rule).

However, the chain rule is embedded in the legs-uncrossed version of...

... the product rule. (Straight continuous lines still differentiating down and integrating up with respect to x.)

The general drift is...

Then...