(declare-function math-parse-date "calc-forms" (math-pd-str))
(declare-function math-lessp "calc-ext" (a b))
(declare-function math-compare "calc-ext" (a b))
+(declare-function math-zerop "calc-misc" (a))
(declare-function calc-embedded-finish-command "calc-embed" ())
(declare-function calc-embedded-select-buffer "calc-embed" ())
(declare-function calc-embedded-mode-line-change "calc-embed" ())
;; (YEAR MONTH DAY math-date-from-gregorian-dt(YEAR MONTH DAY)) for speed.
(defcustom calc-gregorian-switch nil
"The first day the Gregorian calendar is used by Calc's date forms.
-This is `nil' (the default) if the Gregorian calendar is the only one used.
+This is nil (the default) if the Gregorian calendar is the only one used.
Otherwise, it should be a list `(YEAR MONTH DAY)' when Calc begins to use
the Gregorian calendar; Calc will use the Julian calendar for earlier dates.
The dates in which different regions of the world began to use the