Jupyter Kernel: Functions cannot be called in following cells

If a variable is defined in cell 1, it can be used in the following cell.

Example:

cell 0: foobar = 3, cell 1: print(foobar). This will work without any issue and output 3.

However, if a function is defined in cell 0, it cannot be called in cell 1.

Examples:

cell 0: some_function(x)=2*x; print(some_function(10)) --> works without problem and outputs 20.

cell 0: some_function(x)=2*x, cell 1: print(some_function(10)) --> No output at all.