Let $R$ be a relational schema and let $\backslash alpha\; \backslash subseteq\; R$ and $\backslash beta\; \backslash subseteq\; R$ (subsets). The multivalued dependency
$\backslash alpha\; \backslash twoheadrightarrow\; \backslash beta$
(which can be read as $\backslash alpha$ multidetermines $\backslash beta$) holds on $R$ if, in any legal relation $r(R)$, for all pairs of tuples $t\; \_1$ and $t\; \_2$ in $r$ such that $t\; \_1()=t\; \_2()$, there exist tuples $t\; \_3$ and $t\; \_4$ in $r$ such that

$t\; \_1()\; =\; t\; \_2\; ()\; =\; t\; \_3\; ()\; =\; t\; \_4\; ()$
$t\; \_3()\; =\; t\; \_1\; ()$
$t\; \_3(-\; \backslash beta)\; =\; t\; \_2\; (-\; \backslash beta)$
$t\; \_4()\; =\; t\; \_2\; ()$
$t\; \_4(-\; \backslash beta)\; =\; t\; \_1\; (-\; \backslash beta)$