ocaml + some tex updates

nvim/ultisnips/tex.snippets

@@ -130,6 +130,11 @@ snippet ali "Align" bA
 \end{align*} $0
 endsnippet
 
+context "math()"
+snippet \\\ "Backslash" Ai
+\backslash
+endsnippet
+
 context "math()"
 snippet => "Implies" Ai
 \implies
@@ -270,12 +275,12 @@ endsnippet
 
 context "math()"
 snippet uuu "Big cup" iA
-\bigcup{${1:i \in ${2: I}}} $0
+\bigcup_{${1:i \in ${2: I}}} $0
 endsnippet
 
 context "math()"
 snippet nnn "Big cap" iA
-\bigcap{${1:i \in ${2: I}}} $0
+\bigcap_{${1:i \in ${2: I}}} $0
 endsnippet
 
 context "math()"
@@ -401,6 +406,11 @@ snippet '(?<!\\)(alpha|beta|gamma|Delta|delta|epsilon|zeta|eta|Theta|theta|iota|
 \\`!p snip.rv = match.group(1)`
 endsnippet
 
+context "math()"
+snippet 'emptyset' "Emptyset" rwA
+\varnothing
+endsnippet
+
 context "math()"
 snippet '(?<!\\)xxi' "Xi" rwA
 \xi