legend: Add Legends to Plots
In GMD: Generalized Minimum Distance of distributions

This function can be used to add legends to plots. Note that a call to the function locator(1) can be used in place of the x and y arguments.

legend(x, y = NULL, legend, fill = NULL, col = par("col"),
  border = "black", lty, lwd, pch, angle = 45, density = NULL,
  bty = "o", bg = par("bg"), box.lwd = par("lwd"), box.lty = par("lty"),
  box.col = par("fg"), pt.bg = NA, cex = 1, pt.cex = cex,
  pt.lwd = lwd, xjust = 0, yjust = 1, x.intersp = 1, y.intersp = 1,
  adj = c(0, 0.5), text.width = NULL, text.col = par("col"),
  merge = do.lines && has.pch, trace = FALSE, plot = TRUE, ncol = 1,
  horiz = FALSE, title = NULL, inset = 0, xpd, title.col = text.col,
  title.adj = 0.5, seg.len = 2)

`x`	the x coordinates to be used to position the legend.
`y`	the y coordinates to be used to position the legend. `x` and `y` can be specified by keyword or in any way which is accepted by `xy.coords`: See ‘Details’.
`legend`	a character or expression vector. of length >= 1 to appear in the legend. Other objects will be coerced by `as.graphicsAnnot`.
`fill`	if specified, this argument will cause boxes filled with the specified colors (or shaded in the specified colors) to appear beside the legend text.
`col`	the color of points or lines appearing in the legend.
`border`	the border color for the boxes (used only if `fill` is specified).
`lty`	the line types for lines appearing in the legend.
`lwd`	the line widths for lines appearing in the legend. One of `lty` and `lwd` must be specified for line drawing.
`pch`	the plotting symbols appearing in the legend, either as vector of 1-character strings, or one (multi character) string. Must be specified for symbol drawing.
`angle`	angle of shading lines.
`density`	the density of shading lines, if numeric and positive. If `NULL` or negative or `NA` color filling is assumed.
`bty`	the type of box to be drawn around the legend. The allowed values are `"o"` (the default) and `"n"`.
`bg`	the background color for the legend box. (Note that this is only used if `bty != "n"`.)
`box.lwd`	the line type for the legend box.
`box.lty`	the line width for the legend box.
`box.col`	the color for the legend box.
`pt.bg`	the background color for the `points`, corresponding to its argument `bg`.
`cex`	character expansion factor relative to current `par("cex")`.
`pt.cex`	expansion factor(s) for the points.
`pt.lwd`	line width for the points, defaults to the one for lines, or if that is not set, to `par("lwd")`.
`xjust`	how the legend is to be justified relative to the legend x location. A value of 0 means left justified, 0.5 means centered and 1 means right justified.
`yjust`	the same as `xjust` for the legend y location.
`x.intersp`	character interspacing factor for horizontal (x) spacing.
`y.intersp`	the same for vertical (y) line distances.
`adj`	numeric of length 1 or 2; the string adjustment for legend text. Useful for y-adjustment when `labels` are plotmath expressions.
`text.width`	the width of the legend text in x (`"user"`) coordinates. (Should be positive even for a reversed x axis.) Defaults to the proper value computed by `strwidth(legend)`.
`text.col`	the color used for the legend text.
`merge`	logical; if `TRUE`, merge points and lines but not filled boxes. Defaults to `TRUE` if there are points and lines.
`trace`	logical; if `TRUE`, shows how `legend` does all its magical computations.
`plot`	logical. If `FALSE`, nothing is plotted but the sizes are returned.
`ncol`	the number of columns in which to set the legend items (default is 1, a vertical legend).
`horiz`	logical; if `TRUE`, set the legend horizontally rather than vertically (specifying `horiz` overrides the `ncol` specification).
`title`	a character string or length-one expression giving a title to be placed at the top of the legend. Other objects will be coerced by `as.graphicsAnnot`.
`inset`	inset distance(s) from the margins as a fraction of the plot region when legend is placed by keyword.
`xpd`	if supplied, a value of the graphical parameter 'xpd' to be used while the legend is being drawn.
`title.col`	color for `title`.
`title.adj`	horizontal adjustment for `title`: see the help for `par("adj")`.
`seg.len`	the length of lines drawn to illustrate `lty` and/or `lwd` (in units of character widths).