name 'K' is not defined

[Omar-Farhath]

When I tried to execute the main program, I received a name error.

name 'K' is not defined

Call arguments received by layer "sqrt_3b" (type Lambda): • inputs=tf.Tensor(shape=(None, 4, 4, 256), dtype=float32) • mask=None • training=None

I received this error.

Why am I getting this error and how do I solve this ?