Consolidation of derivation rules on Section B.3.2

PDR5 and PDR6 could be combined in one as below:

• PDR5 from "If two relationships p(a,b):S and q(c,a):T exist, with S being a structural relationship and T being a dependency relationship, then a relationship r(c,b):T might be derivable." to "If two relationships p(a,b):S and q(c,a):T exist, with S being a structural relationship and T being a dependency relationship, then a relationship r(c,b):T, with the same direction as q, might be derivable."
• remove PDR6