Symbolize the following, which require frequent use of the horseshoe. Use only the abbreviations provided.
J=John will make supper; W=Mary is working late; M=Mary will make supper; John=is working late; H=John is very hungry; B=John's boss requires his working late; O=It is a holiday; D=John washes the dishes
a) Mary will make supper if John is working late
b) John works late if and only if Mary does not
c) John will not work late unless his boss requires it
d) John or Mary will work later, but not both.