If P: R2 -> R is defined by p(x,y) = x . y, then(adsbygoogle = window.adsbygoogle || []).push({});

Dp(a,b)(x,y) = bx + ay.

Please tell me in words how to read Dp(a,b)(x,y). Is this a product? a composition of functions? Is this the differential of p(x,y) at (a,b)? If that's the case, why does the text also state:

If s: R2 -> R is defined by s(x,y) = x + y, then Ds(a,b) = s. (i.e. not "Ds(a,b)(x,y) = ...").

Thank you!

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# Chain rule: please translate

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