The last one on the chain.
The other activations on the chain are awaiting results before proceeding. (The inactive circles have already returned results and will never again represent executing code.)
Here are some equal strings:
"abc" equals "abc" "abc de" equals "abc de"
And here are some unequal strings:
"ab" !equals "abc" "abC" !equals "abc" "abc" !equals "aBc"
Let us try to find rules for string equality.
Is the string ""
equal to the string ""
?
(Is the empty string equal to the empty string?)