+/***
+ * [[defs]]
+ * Definitions
+ * -----------
+ ***/
+
+/**
+ * Find the first element not lower than @x in the sorted array @ary of @N elements (non-decreasing order).
+ * Returns the index of the found element or @N if no exists. Uses `ary_lt_x(ary,i,x)` to compare the @i'th element with @x.
+ * The time complexity is `O(log(N))`.
+ **/