fixed dependencies

vendor/github.com/go-latex/latex/mtex/symbols/set.go

@@ -0,0 +1,43 @@
+// Copyright ©2020 The go-latex Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package symbols
+
+import (
+	"sort"
+)
+
+type Set map[string]struct{}
+
+func NewSet(vs ...string) Set {
+	o := make(Set, len(vs))
+	for _, k := range vs {
+		o[k] = struct{}{}
+	}
+	return o
+}
+
+func (set Set) Has(k string) bool {
+	_, ok := set[k]
+	return ok
+}
+
+func (set Set) Keys() []string {
+	keys := make([]string, 0, len(set))
+	for k := range set {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	return keys
+}
+
+func UnionOf(sets ...Set) Set {
+	o := make(Set, len(sets))
+	for _, set := range sets {
+		for k := range set {
+			o[k] = struct{}{}
+		}
+	}
+	return o
+}