$\gtrdot$ and $\lessdot$ are operators belonging from the Operator Precedence Languages.
Given two terminals $a,~ b$, for any non-terminals $A, ~B,~ C$ and mixed terminal/non-terminal strings $α,~ β, ~γ$, we say
$(i)~~$ $\bf a$ yields precedence to $\bf b$ $~(a \lessdot b)~$ if there exists a rule $~A → αaCβ~$, s.t. a string $~Baγ~$ or $~aγ~$ derives from $~C~$ in any number of passes;
$(ii)~~$ $\bf a$ is equal in precedence to $\bf b$ $~(a \doteq b)~$ if there exists a rule $~A → αaCbβ~$ or $~A → αabβ~$;
$(iii)~~$ $\bf a$ takes precedence over $\bf b$ $~(a \gtrdot b)~$ if there is a rule $~a → αCbβ~$, s.t. $~γaB~$ or $~γa~$ derives from $~C~$.
In practice, $~a \lessdot b~$ if $b$ is the beginning of $a$ right hand side (rhs); $~(a \doteq b)~$ if they belong to the same rhs; $~(a \gtrdot b)~$ if a is the end of a rhs.
For more details you may find the following references:
$1.~~$ "Precedence Automata and Languages" by Lonati V., Mandrioli D., Pradella M.
$2.~~$ "Word- and Tree-Based Temporal Logics for Operator Precedence Languages" by Michele Chiari, Dino Mandrioli, and Matteo Pradella
$3.~~$ "Mathematical Operators"
$4.~~$ Operator-precedence grammar