Exception: Failure "Closing bracket expected".

[logisin]

I did the following:
1)git clone https://github.com/Tipoca/handbook-of-practical-logic-and-automated-reasoning.git
2)cd handbook-of-practical-logic-and-automated-reasoning
3)make
After the interactive prompt of ocaml responds I give the following:
4)<<(x1+x2+x3) * (1+2+3*x+y)>>;;
And I get the message:
Exception: Failure "Closing bracket expected".

Any ideas what I'm doing wrong?
PS: There many warnings that & is deprecated and also that
File "atp_interactive.ml", line 1234, characters 2-971:
Warning 8: this pattern-matching is not exhaustive.
Here is an example of a value that is not matched:
("", _)