Add() in cnn refers to?

#1

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IN THE CNN CODE
WHAT DOES THE BELOW LINE REFERS TO (ADD()-WHY DO WE USE THIS FUNCTION??)

out = add([shortcut, out])

#2

please reply to my doubt

#3

add([1,2], [3,4]) will give [4, 6]

See here for more details: https://www.tensorflow.org/api_docs/python/tf/keras/layers/Add