| Number | Name | Date | Kind |
|---|---|---|---|
| D328475 | Gould et al. | Aug 1992 | |
| 3784205 | Cross, Jr. | Jan 1974 | |
| 3891217 | Geary et al. | Jun 1975 | |
| 4133538 | Ambrose | Jan 1979 | |
| 4173833 | Rosenblatt | Nov 1979 | |
| 4184685 | Wilson | Jan 1980 | |
| 4955615 | Eck | Sep 1990 | |
| 5560611 | Kim | Oct 1996 |
| Number | Date | Country |
|---|---|---|
| 3127075 | Jan 1983 | DEX |
| 2227422 | Aug 1990 | GBX |
| Entry |
|---|
| (ISBN-0534142869) Gustafson and Frisk, Functions and Graphs, Second Edition, Brooks/Cole Publishing Company, CA, 1987, pp. 64-65. |